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Wilms tumor accounts for 87% of pediatric renal masses. Its peak incidence is at 3–4 years of age. Patient age in this case is outside of the typical range. Renal cell carcinoma is also a consideration in this age group.

Malignancy is found in around 5% of patients with vasculitis. The reason for this association is unclear, although postulated mechanisms include immune complex formation with tumour antigens, shared tumour and vessel wall antigens, and impaired clearance of normally produced immune complexes. Additionally, some research suggests a viral etiology.

In this patient the vasculitis was present prior to the development of Wilm tumor. The vasculitis has features of polyarteritis nodosa, such as multiple aneurysms and stenoses of medium size vessels but lack of renal artery involvement is unusual.

Polyarteritis nodosa (PAN) is a systemic illness characterized by necrotizing inflammation of small- and medium sized arteries, leading to aneurysm formation. It is associated with hepatitis B virus (HBV) in about 7% of cases. The most common clinical symptoms are persistent fever, weight loss, and polyarthralgia (the patient in this case did not report these symptoms).

PAN is rare in childhood and represents one of the rarest vasculitides in children. Ozen et al. defined musculoskeletal and renal involvement as the major diagnostic criteria for PAN in childhood. Ten additional minor criteria were also defined: (1) cutaneous findings, 2) gastrointestinal involvement, (3) peripheral neuropathy, (4) central nervous system involvement, (5) hypertension, (6) cardiac involvement, (7) lung involvement, (8) constitutional symptoms, (9) presence of acute-phase reactants, and (10)presence of hepatitis B surface antigen. They proposed that the presence of five of these criteria, including at least one major criterion, is highly suggestive of PAN in childhood. The patient in this case does not meet all of these criteria, but the appearane and involvement of the mesenteric vessels still suggests PAN as the most likely diagnosis.

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